Area Forecast Discussion
Issued by NWS Portland, ME

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181 FXUS61 KGYX 221520 AAB AFDGYX Area Forecast Discussion...UPDATED National Weather Service Gray ME 1120 AM EDT Tue Aug 22 2017 .SYNOPSIS... High pressure retreats well offshore today. A strong cold front will move across the region tonight and early Wednesday accompanied by showers and thunderstorms. High pressure and drier air follows the front Wednesday night through Friday. && .NEAR TERM /UNTIL 7 PM THIS EVENING/...
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1112 AM Update: Made some changes to the overall evolution of precipitation chances this afternoon and evening...employing information from late morning runs of the HRRR and the 12Z NAM nest. Biggest changes are to reduce PoP coverage through early-mid afternoon with forcing still well off to the west. Have seen some convection fire along advancing thetae plume in the WAA environment...but these have been struggling as they advance east. Have also tried to time primary threat of severe weather...which looks to be in the 7pm - 2am timeframe. Am in agreement with current SPC outlook...with robust squall line reaching CT valley around 7-8 pm. No other significant changes at this time. 905 AM...Minor ESTF update to reflect the current mesonet in near term grids. Prev disc... 650 am Update: Skies mostly clear early this morning with patchy fog along the CT River Valley that will burn off in the next few hours. Input latest mesonet data with no forecast changes needed at this time. Previous Discussion: Some patchy early morning Valley fog along the Ct River otherwise a mostly sunny start to the day. Considerable moisture advection with very high PW`s and increasing shear will result in rapid destabilization of the atmosphere during the afternoon. This will result in strong to possibly severe thunderstorms to develop first across NH and then spread east into Maine by mid to late afternoon. Temps will be very warm with highs in the mid to upper 80s. Pooling dewpoints reaching near 70 will make it feel very muggy.
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&& .SHORT TERM /7 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... The cold front and upper trof press east tonight allowing the strong thunderstorms to continue in advance through most of the evening before slowly weakening later at night and becoming more widely scattered. The cold front moves off the coast Wednesday morning allowing for cooler, drier air, and clearing in its wake during Wed as high pressure builds in from the west. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... The system that will bring rain to us today and Wednesday will be its way out on Thursday. The parent surface circulation will be well north in Quebec while the cold front which sweeps through Wednesday morning will be well offshore. Aloft a deep trough will continue to spin bringing occasional clouds and isolated showers to the mountains...mainly in the heat of the day each afternoon. However, for the most part large sprawling high pressure which has been dominating the central states will move into and strengthen over New England. This along with drier air will suppress any further activity despite the persistent troughing aloft. The exception to this may be a back door cold front which could spark off a few showers on Sunday. Temperatures will generally be close to normal values /mid 60s north to mid 70s south/ for highs. Overnight lows should drop into the 40s and 50s most nights under partial to complete clearing and light winds. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... Short term...Patchy early morning fog in the CT River Valley otherwise VFR this morning. Conditions lowering to MVFR and locally IFR in developing afternoon and evening thunderstorms. Some of the storms will be strong with gusty winds and possible hail. The thunderstorms will weaken later in the evening but scattered showers with MVFR conditions will continue until the passage of the cold front by Wednesday morning. Conditions will improve to VFR behind the FROPA Wednesday. Long Term...Some patchy fog is possible early Thursday morning...especially where it has rained. Also some mountain valleys may radiate to the dew point each morning Friday and Saturday. && .MARINE... Short Term...Winds and seas will increase later today and tonight as the south to southwest flow increases ahead of the approaching cold front. SCA conditions will develop this afternoon and continue through tonight and into Wednesday. The cold front will cross the waters Wednesday allowing a gradually wind shift to the west helping knock down the seas by later in the day. Long Term...Winds and seas will remain calm for the remainder of the week. && .TIDES/COASTAL FLOODING... We`re in the period of high astronomical tides for the month of August. The remaining high tide of potential concern (referencing Portland Harbor where flood stage is 12.0 ft MLLW) is: 1231 AM Wednesday. 11.1 ft MLLW Tonight`s high tide (1231 AM Wednesday) could see some splashover and minor beach erosion as onshore flow and seas increase ahead of an approaching cold front. && .GYX WATCHES/WARNINGS/ADVISORIES... ME...None. NH...None. MARINE...Small Craft Advisory from 8 PM this evening to 8 AM EDT Wednesday for ANZ151-153. Small Craft Advisory from 3 PM this afternoon to 8 AM EDT Wednesday for ANZ150-152-154. && $$ NEAR TERM...Arnott is the U.S. government's official web portal to all federal, state and local government web resources and services.